It was my JRE that was broken, and now the problem is fixed. Nothing to do with Jedit (apologies for the confusion).

The JDK I'm using (j2sdk-1_4_2_04-windows-i586-p.exe) installs both the JRE and the JDK. However, there is an issue if you intend to install the JDK in a folder other than the default, which is: 'c:\program files'. In that case, the JDK installs correctly, but the JRE will still install in 'program files' regardless. This creates potential conflicts with some programs (like Jedit), and the 'Java Home' variable in the registry will be incorrectly reflected as within 'program files'.

If you need to install the JDK in a directory other than the default, you can work around this issue by first dowloading and installing the JRE by itself. Select 'custom' install and indicate the name of the folder where you want the JRE installed. Then download and install the JDK.

If you have already installed the JDK and there is already a 'java' folder under 'c:\program files', first uninstall the JRE using Control Panel's Add/Remove Programs, and then download and reinstall the JRE by itself. Select 'custom' install and indicate the name of the folder where you want the JRE installed.

When the installation is complete, check that there is no 'java' folder under 'c:\program files'.